Since November 2021, Greece’s prime minister and the British Museum have been holding back-room talks about the potential return of at least some of the Parthenon Marbles, a collection of antique treasures that once decorated the famed pillared temple in Athens.

The collection, which includes statues of Greek gods and carved friezes, was taken from Greece in the early 1800s by Lord Elgin, a British aristocrat. They have been at the London museum ever since.

The prime minister, Kyriakos Mitsotakis, has met several times with George Osborne, a former chancellor of the Exchequer who is now chairman of the British Museum.. The rapport between Mitsotakis and Osborne has widely been seen as one reason the talks have progressed so far.

But on Sunday, Greece holds an election and the talks have been postponed until the result of the vote is clear.

Mitsotakis told reporters last week that if he were re-elected he would “pick up again the momentum and build upon the progress that we have made” in the discussions.

If he does not win, how will the future of the marbles be affected?

At the start of this year, Mitsotakis and his New Democracy party were cruising to re-election, according to Nick Malkoutzis, the editor of the Greek politics website MacroPolis.

But on March 1, a head-on collision between a freight train and a passenger service killed at least 57 people and injured scores of others. After the disaster, the deadliest ever on Greece’s rail network, tens of thousands of demonstrators took to the streets to protest successive governments’ lack of investment in train safety.

After initially blaming the accident on a “tragic human error,” Mitsotakis asked the Greek people for forgiveness for the chronic failings.

In the fallout from the tragedy, New Democracy lost several percentage points in opinion polls, Malkoutzis said. The party now seems set to take about 36 percent of the vote on Sunday, probably scuppering its hopes of an outright win, which would have been difficult even before the crash.

Malkoutzis said that a second round of voting would most likely be needed. In that case, under Greek law, the election rules change, and the prime minister would be hopeful of securing a majority. But, Malkoutzis said, “low turnout or shifting voter patterns” could still make a coalition government necessary.

If New Democracy does need the help of another party to govern, Malkoutzis said that the most likely partner would be a center-left alliance called Pasok-Kinal.

Nikos Orfanos, a theater director and a spokesman on culture for Pasok-Kinal, said in a telephone interview that returning the marbles was vital because the artifacts were part of Greece’s national identity.

But, he added, “a matter of such national importance, with national aspects, should not become the subject of secret diplomacy.” Orfanos said that any deal should be discussed with the Greek Parliament, adding that a prime minister must not simply present “a take it or leave it deal” to lawmakers without them having a say.

The main opposition party in Greece is the leftist Syriza, led by Alexis Tsipras, who was prime minister from 2015 to 2019. Syriza is expected to come second this weekend, with polls suggesting it will secure about 29 percent of the vote.

A surprise Syriza victory could complicate negotiations with the British Museum. The party has long opposed the discussions about the marbles, saying that Britain’s government should return the collection immediately.

Sia Anagnostopoulou, the party’s spokeswoman on culture, said by email in January that the sculptures had to be “returned, reunified and exhibited in their entirety” in Athens. Her party would not accept only a portion of the collection being returned on loan, she added — one of the options under discussion.

When Syriza was last in government, the party focused on working with the United Nations to try to pressure Britain into returning the marbles.

Pressure is growing on the British Museum to deal with the many contested artifacts in its collection. In recent years, some major Western museums have begun returning high-profile items. In December, German museums began returning a collection of priceless Benin Bronzes to Nigeria.

Some fragments of the Parthenon held in other countries were already heading back to Greece. In March, three 2,500-year-old pieces of the Parthenon that had been in the Vatican’s collections were returned to the Acropolis Museum in Athens. And this month, it emerged that the Kunsthistorisches Museum in Vienna was in talks with the Acropolis Museum about a loan agreement involving two more Parthenon fragments.

Nikos Dendias, the Greek foreign minister, said in a news conference that the Austrian talks were of “huge importance” and would help “create a momentum which we could use in our discussions in London” about the British Museum’s holdings.

The British Museum says on its website that it is in discussions with Greece over a new “Parthenon partnership” in which items might be shared or lent between the two countries. But its officials regularly point out that the museum cannot return items permanently to Greece, even if it wanted to, because British law bars it from removing items from its collection.

Few British politicians are lining up to change that law. In March, Prime Minister Rishi Sunak told reporters, “The U.K. has cared for the Elgin Marbles for generations.” The British Museum’s collection was protected by law, he said, adding, “We have no plans to change it.”